[jtoy4eva]

when you have 2 cyclohexanecarbaldehyde reacting with hydroxide it undergoes aldol addition (aldehyde) reaction

will the product be a molecule with (describing) two cyclohexane on each side with two C-C bond in between and a C=O on the central C ??

isnt the aldol addition react with the alpha hydrogen? but the alpha hydrogen is the one of the C in the cyclohexane...

confused ...

[spirochete]

The product you described is not accurate.  You are on the right track with thinking about the location of the alpha hydrogen.  The tertiary alpha hydrogen is lost, making a nucleophile that attacks the ketone carbon on another molecule.  This is kind of a funny reaction because the intial Beta-Ketone-Alcohol can't dehydrate to give a double bond in the expected location.  Normally the double bond always forms in a paticular location because it's energetically favorable. 

Do you see why the alcohol normally dehydrates in a paticular way, and why it can't do that in this case? 

[jtoy4eva]

my mistake sorry

i meant a OH on the central C of the two C-C bond connecting the two cyclohexane

anyway so this product is the exact product from 2 cyclohexanecarbaldehyde + hydroxide ion?

[spirochete]

yes that sounds right, as long as you know you're leaving out the obvious aldehyde group on one of the rings.

[jtoy4eva]

is there a chance that 2 cyclohexanecarbaldehyde reacting with hydroxide ion but undergoes a reaction other than an aldol addition?

[spirochete]

Maybe a tiny tiny insignificant amount of geminal diol?  That would be the carbonyl replaced by a carbon with two hydroxyl groups bonded to the one carbon.  Really though it's a straightforward reaction  andI don't see any side reactions under those conditions.